1. Field of the Invention
The present invention relates generally to a gas turbine fuel system and more specifically to a gas turbine fuel system comprising a fuel oil distribution control system, a fuel oil purge system, a purging air supply system and a fuel nozzle wash system in which fuel oil distribution is controlled to be done uniformly to a plurality of fuel nozzles with enhanced reliability of fuel distribution and residual oil in fuel pipings and nozzles when gas turbine operation is changed over to gas fuel from oil fuel is purged effectively so that load change caused by burning of the residual oil at the time of purging is prevented.
2. Description of the Prior Art
FIG. 9 is a block diagram of an entire gas turbine fuel system comprising therein a fuel oil supply system, a fuel oil purge system, a purging air supply system and a compressor outlet wash system in the prior art. In FIG. 9, a combustor X comprises therein a plurality, about 20 pieces for example, of fuel nozzles X.sub.1, X.sub.2 disposed along an inner periphery thereof. The fuel nozzles X.sub.1 are supplied with fuel gas from a fuel gas supply system and the fuel nozzles X.sub.2 are supplied with fuel oil from a fuel oil supply system G. These gas and oil are changed over to either one thereof to be supplied into the combustor X for combustion. The fuel oil supply system G, as mentioned, is a system for supplying therethrough fuel oil and a fuel oil purge system H is a system for purging oil remaining in the piping system or fuel nozzles when the fuel is changed over to gas from oil. A purging air supply system J supplies therethrough a purging air into the fuel oil purge system H. A compressor outlet wash system K is a system for injecting water into a compressor outlet for washing this compressor outlet which communicates with the combustor. Description will be made further on each of the above systems.
The fuel oil supply system G will be described first. In the gas turbine, a stable combustion is required for a wide range of fuel flow rate from ignition to power output. Especially, in the low fuel flow rate range at the time of ignition etc., there is only a small differential pressure of the fuel nozzles in the combustor, which results in an unstable combustion. In the recent gas turbine, there are provided a large number of fuel nozzles of about 20 pieces and there arises unbalance in the fuel flow rate by the influence of head difference between upper ones and lower ones of the fuel nozzles which are disposed up and down. For this reason, a flow divider is provided so that fuel is divided to be supplied uniformly to each of the fuel nozzles. But this flow divider is not necessarily of a sufficient reliability and thereby often caused are troubles in the fuel system.
FIG. 10 is a diagrammatic view of the fuel oil supply system G in the prior art. In FIG. 10, fuel oil is controlled of flow rate by a flow control valve 11 to then flow through a piping 12 and enters a flow divider 80 to be divided there to flow through a plurality of pipings 82 of about 20 pieces and to be supplied into each of the fuel nozzles X.sub.2 of the combustor X. The gas turbine fuel nozzles X.sub.2 are disposed in about 20 pieces along a circumference and there is a head difference of about 4 m between the nozzles of upper position and those of lower position. This head difference produces unbalance in the fuel flow rate, especially in the low fuel flow rate range at the time of ignition. For this reason, the flow divider 80 is provided but this flow divider 80 is constructed such that a spiral shaft is disposed in a cylindrical body and while this shaft is rotated, fuel oil is flown into the cylindrical body to be divided to flow through each of the plurality of pipings 82 uniformly. A motor 81 is operated only in the operation start time for ensuring a smooth start of rotation of the flow divider 80.
FIG. 11 is a view showing relation between load transition (fuel flow rate) and system differential pressure in the prior art gas turbine, wherein as load increases, fuel flow rate increases from gas turbine ignition time t.sub.0 to rated speed (no load) arrival time t.sub.1 and further to time t.sub.2 when the system differential pressure including nozzle differential pressure comes to a necessary nozzle differential pressure V.sub.1. That is, during the time T from t.sub.0 to t.sub.2, the system differential pressure does not reach the necessary nozzle differential pressure V.sub.1 but it reaches V.sub.1 at time t.sub.2 to increase more thereafter. Accordingly, the nozzle differential pressure is low during the time shown by T and if there is a head difference between said plurality of fuel nozzles, there occurs unbalance of fuel flow rate between each of the fuel nozzles, hence the flow divider 80 is operated so that the unbalance of the fuel oil between each of the fuel nozzles may be eliminated. But this flow divider 80 has a very small gap between the inner rotational body and the stationary portion for its function and this makes control of foreign matters difficult and has been often causes of troubles in the fuel system.
Next, the fuel oil purge system H will be described. FIG. 12 is a diagrammatic view of the fuel oil purge system in the prior art at the time when the gas turbine fuel is changed over. In FIG. 12, numeral 1 designates a flow control valve in a fuel gas system, numeral 2 designates a piping therefor, numeral 3 designates a fuel gas distributor, which distributes the fuel gas to the plurality of fuel nozzles X.sub.1 and numeral 4 designates a plurality of pipings, which supply therethrough the fuel gas from the fuel gas distributor 3 to the respective fuel nozzles X.sub.1.
Numeral 11 designates a flow control valve in a fuel oil system, numeral 12 designates a piping therefor, numeral 13 designates a header, which distributes the fuel oil from the piping 12 to the plurality of fuel nozzles X.sub.2 and numeral 14 designates a plurality of pipings, which are connected to the header 13 and supply therethrough the fuel oil distributed by the header 13 to the respective fuel nozzles X.sub.2. Numeral 26 designates a purging air system piping, numeral 25 designates an opening/closing valve, numeral 23 designates a drain valve piping and numeral 24 designates an opening/closing valve therefor. Combustor X comprises therein the fuel nozzles X.sub.1, X.sub.2.
In the mentioned system so constructed, while the operation is done with the fuel oil being burned, the fuel oil flowing through the flow control valve 11 and the piping 12 is distributed by the header 13 to flow through the plurality of pipings 14 to the respective fuel nozzles X.sub.2. The fuel oil so distributed is injected into the combustor X from the fuel nozzles X.sub.2 for combustion there.
When the operation is done with the fuel being changed over to gas from oil, the flow control valve 11 is closed and the fuel gas is led instead into the piping 2 to be supplied to the fuel nozzles X.sub.1 through the fuel gas distributor 3 and the piping 4. In this case, the previous fuel oil remains as it is in the pipings 12, 14 and this fuel oil, if left there, is carbonized to stick there with a fear to cause blockage of the pipings and nozzles. Hence, it is necessary to remove such residual oil when the fuel is changed over to gas.
Thus, the opening/closing valve 25 is opened so that purging air 40 is led into the piping 12 from the purging air system piping 26. The purging air 40 enters the header 13 through the piping 12 to then flow through the pipings 14 to the fuel nozzles X.sub.2 to be blown into the combustor X. Thereby, the fuel oil which remains in the piping 12, header 13, pipings 14 and fuel nozzles X.sub.2 is all discharged into the combustor X. This purging of the residual oil is done while the operation is continued with the fuel gas being supplied and burned in the combustor X. But there is a considerable quantity of such residual oil itself in the piping 12, header 13, pipings 14 and fuel nozzles X.sub.2 and also there are provided a large number of the fuel nozzles X.sub.2 and same number of the pipings 14 connected to the respective fuel nozzles X.sub.2. Accordingly, if the residual oil in these portions is all discharged into the combustor X and the operation is continued with the fuel gas so changed over, then the fuel oil so discharged into the combustor X burns so that the fuel increases beyond a planned supply value, which elevates combustion temperature to cause a large load change. Hence, realization of a fuel oil purge system which does not cause such a load change has long been desired.
Next, the purging air supply system J will be described. In the recent gas turbine, there is realized an operation system wherein fuel is changed over to gas from oil, as mentioned above. This operation system comprises therein both of fuel oil system and fuel gas system and it is necessary to purge fuel pipings and nozzles on the side not used. Especially in the fuel oil system, oil remains in the pipings and, if left as it is, is carbonized to stick there and there is a fear of blockage of the pipings and nozzles.
FIG. 13 is a diagrammatic view of the purging air supply system J in the prior art gas turbine. In FIG. 13, numeral 110 designates a gas turbine, numeral 42 designates a piping for taking out therethrough outlet air of air compressor and numeral 90 designates an air cooler, which comprises therein a multiplicity of tubes communicating with the piping 42. Numeral 91 designates a motor for rotating a fan 92 to thereby supply air to the air cooler 90 and numeral 43 designates a piping connecting to outlet of the air cooler 90. Numeral 93 designates also a piping, which diverges from the piping 42 for obtaining air of the purge system and numeral 94 designates a cooler using water 95 for cooling the air from the piping 93. Numeral 96 designates a piping connected to outlet of the cooler 94, numeral 97 designates a drain separator, numeral 98 designates a piping connected to outlet of the drain separator 97, numeral 53 designates a pressure elevation compressor and numeral 99 designates a piping connected to outlet of the pressure elevation compressor 53. Numeral 100 designates a cooling using water 101 for cooling the air which has been heated to a high temperature by pressure elevation at the pressure elevation compressor 53 to an appropriate temperature as a fuel nozzle purging air. Numeral 48 designates a piping for supplying therethrough the air which has been cooled to the appropriate temperature as the purging air at the cooler 100.
In the mentioned system so constructed, the air of the compressor outlet of about 400.degree. C. is cooled at the air cooler 90 to about 200 to 250.degree. C. to be supplied into the gas turbine 110 as a rotor cooling air through the piping 43, wherein a portion of the air of the compressor outlet diverges from the piping 42 and is led into the cooler 94 through the piping 93 to be cooled to about 130.degree. C. to be then sent to inlet of the pressure elevation compressor 53. This air is removed of drain by the drain separator 97 disposed between the pipings 96 and 98. Then, the air is compressed to a predetermined pressure at the pressure elevation compressor 53 and its temperature is also elevated to about 200.degree. C. This air of about 200.degree. C. is led into the cooler 100 through the piping 99 to be cooled there to about 150.degree. C. which is appropriate for the purging and is then supplied to each of the fuel systems through the piping 48 as the purging air.
Thus, in the purging air supply system, as the inlet temperature of the pressure elevation compressor 53 becomes high, there is provided the cooler 94 for cooling the compressor outlet air of about 400.degree. C. to about 100 to 130.degree. C. Also, as the air, when compressed at the pressure elevation compressor 53, is heated to about 200.degree. C., it is cooled again at the cooler 100 to about 150.degree. C. In this kind of system, therefore, there are needed the coolers 94, 100 or the like, which requires large facilities and spaces therefor. Hence, it has been needed to improve these shortcomings and to attain cost reduction.
Next, the compressor outlet washing system K will be described. FIG. 14 is a diagrammatic view of the compressor outlet wash system in the prior art. In FIG. 14, letter X designates a combustor, numeral 112 designates a compressor outlet and numeral 113 designates a manifold for distributing wash water in an annular form, as described later. Numeral 114 designates a plurality of wash nozzles, which are provided along periphery of the manifold 113 for injecting therefrom wash water into the compressor outlet 112. Numeral 11 designates a flow control valve for fuel oil, numeral 12 designates a piping and numeral 13 designates a header for distributing fuel into a plurality of fuel supply pipings 14. Fuel oil is supplied from the respective fuel supply pipings 14 to a plurality of fuel nozzles X.sub.2.
Numeral 60 designates an air control valve for leading a high pressure air into a wash tank 62 via a piping 61. The wash tank 62 stores therein the wash water for washing interior of the compressor outlet 112. Numeral 63 designates an opening/closing valve, through which the wash water flows to be supplied into the manifold 113 via a piping 64. The wash water supplied into the manifold 113 is injected from the plurality of wash nozzles 114 into the surrounding area for washing the interior of the compressor outlet 112. Numeral 65 designates an opening/closing valve and numeral 66 designates a piping for supplying therethrough the wash water in a necessary quantity into the wash tank 62.
In the gas turbine compressor outlet wash system so constructed, when the compressor outlet 112 is to be washed, the air control valve 60 is opened and the high pressure air is led into the wash tank 62 via the piping 61 so that interior of the wash tank 62 is pressurized. Then, the opening/closing valve 13 is opened and the wash water is supplied into the manifold 113 via the piping 64. The wash water is injected from the wash nozzles 114 for washing the interior of the compressor outlet 112.
On the other hand, as for the gas turbine operation, fuel oil is led into the header 13 via the flow control valve 11 and the piping 12 to be distributed there to flow into the plurality of fuel supply pipings 14 uniformly and is then supplied into the respective fuel nozzles X.sub.2 for combustion.
In the recent gas turbine, there is developed a dual fuel system in which both fuel oil and fuel gas are usable and the fuel is changed over to gas from oil, or to oil from gas, as the case may be. In such a system, if, for example, the operation done by oil is stopped or is continued with the fuel being changed over to gas from oil, the fuel oil remaining in the fuel pipings and nozzles is carbonized to stick there and there arises a fear of blockage of the fuel pipings and nozzles. Thus, attempt is being done for providing large scale facilities by which the fuel pipings and nozzles are purged by air or the like. But these exclusive purging facilities require a large apparatus, which are naturally undesirable from viewpoint of cost reduction.